1. Field of the Invention
The present invention relates generally to prosthetic devices for supporting or maintaining the position of mammalian tissue and the like and replacements therefor, and more particularly relates to a method and apparatus for manufacturing such prosthetic devices.
2. Description of the Prior Art
Surgical meshes are an example of a support device for supporting or reinforcing tissue or muscle, or supporting and/or maintaining the position of natural anatomical structures (e.g. spleens or breast tissue), or certain anatomical replacements (e.g. breast implants).
In the case of supporting and maintaining the position of breast implants, some surgeons cut flat, two dimensional meshes to the desired size and shape creating a formed support device, and then sew them to the desired form during surgery while in the sterile field. Examples of such techniques are described in U.S. Patent Application Publication No. 2006/0030939 having Robert E. Frank as the named inventor, and PCT Patent Application Publication No. 2004/096098 having Jonathan Hamilton, et al. as the named inventors. This activity carries two primary disadvantages. First, cutting the mesh in an operating room creates fine (albeit sterile) dust, a byproduct that is undesirable to have in a clean operating room. Second, and perhaps more importantly, the preparation of a flat mesh into a formed support device takes time and energy; it is well established that minimizing the length of time of a given surgical procedure is a health and cost benefit to all.
In the case of supporting and maintaining the position of other anatomical structures or replacements, such as a spleen or heart, some surgeons use mesh bags, as described in U.S. Pat. No. 4,428,375, which issued to Barry R. Ellman. These mesh bags may be likened to purse strings used to cinch the mesh bag around the structure or the replacement. The final configuration of the mesh bag conforms to the structure it supports, but often has wrinkles and folds. These wrinkles and folds define areas where the support has varied across locations. At the folds and wrinkles, the support is minimal. Furthermore, the wrinkles and folds define areas of increased surface area where adhesions may form and can cause the mesh to migrate, concomitantly causing the mesh to pull on the structure whose position the mesh is meant to maintain. Furthermore, adhesions are known causes of post-surgical pain. The term “wrinkles and folds” used herein connotes any wrinkles, folds, pleats, or the like and any combination thereof that may form in a mesh while the mesh is being used in a surgical procedure.
Some support devices are cumbersome to apply when they do not possess a sufficient resiliency or stiffness property. The shape of such devices, lacking the ability to support their own weight without collapsing, must be manually maintained in order to position the support device and to secure it in place. For example, a mesh knitted as a three dimensional shape made from conventionally sized medical mesh polypropylene fibers will collapse under its own weight. When used in a surgery, this effect is exacerbated as the mesh becomes sullied with blood and other body fluids.
Some patents or published patent applications describe preformed meshes for repairing hernias (i.e. for reinforcing tissue and muscle). These preformed meshes are significantly smaller and have a much less significant preform than a formed support device used for supporting an anatomical structure or replacement. Creating a preformed support device suitable for supporting natural breast tissue or a breast implant using the methods described in the hernia mesh patents or published patent applications may impart pleats or folds into the preformed support device. The presence of pleats and folds creates excess foreign body that is placed into a human body during the surgical procedure which may attribute to serious side effects such as infection and scar formation. Therefore, it is desirable to minimize the amount of foreign body introduced into the body by eliminating any pleats or folds. The term “pleats or folds” connotes any wrinkles, folds, pleats, or the like or any combination thereof that may form in a sheet of material while it is being shaped into a preformed support device.
Anatomical structures and replacements are subject to dynamic loading over a wide array of loading conditions for varied periods of time. For example, conventionally, the mesh bag used to support a spleen is absorbable, while a mesh sheet used for supporting a breast implant is non-absorbable. The support device must be strong and resilient enough to autonomously maintain its form and structure, and additionally the position of the structure or replacement.
U.S. Patent Application Publication No. 2006/0030939 of Frank and PCT Patent Application Publication No. 2004/096098 of Hamilton, et al. describe formed support devices for natural breast tissue and breast implants. The Frank and Hamilton, et al. published applications both describe two dimensional shapes precut into a mesh to facilitate the process of making a formed support device during surgery. However, neither published application describes the creation of a preformed support device.
U.S. Pat. No. 5,954,767, which issued to Philippe Pajotin, et al., and U.S. Pat. No. 6,723,133, which issued to Philippe Pajotin, both describe a preformed curved mesh. Both patents describe meshes having a permanent three dimensional shape formed via a thermoforming process. The specific thermoforming process for forming the mesh described in these patents is not adequate to create a preformed support device capable of supporting a breast implant or natural breast tissue (or other anatomical structure or structural replacement) for long periods of time. The processes disclosed in the Pajotin et al. and Pajotin patents could impart folds or pleats into a preformed support device having a large surface area to cavity opening area ratio. Notably, the processes described in these patents suggest placing the mesh in the mold prior to heating the mesh or the molds. Furthermore, the process disclosed in the '133 Pajotin patent imparts a permanent shape to a mesh by annealing and shrinking (over some, but not all, of the disclosed temperature range). In the manner described in these patents, there is little if any control over the strength and resiliency properties of the mesh. When the mesh is only annealed, its fibers become weaker. When the mesh is annealed and shrunk, the fibers become thicker and the distance between the wales is lessened. It is unclear which process conditions yield a stronger or weaker final mesh. As a point of clarification, the title of the '133 Pajotin patent is “Preformed Curved Prosthesis Having a Reduced Incidence of Developing Wrinkles or Folds.” It is noted that these wrinkles and folds are those that may be introduced to the mesh while the mesh is being used in a surgical procedure. These “wrinkles and folds” are different from the pleats and folds described in the present invention. These pleats and folds refer specifically to those pleats and folds that may be formed during the fabrication process of the preformed support device.
U.S. Pat. No. 6,241,768, which issued to Vishvaroop Agarwal, et al., describes a prosthetic device for repairing hernias that is also formed from a mesh. This device has a preformed curved feature that is formed via a thermoforming process. The forming process and its shortcomings are similar to those described for the '133 Pajotin patent and the '767 Pajotin, et al. patent. It is not clear from the description whether or not the mold is heated before or after the mesh is introduced to it.
Some have attempted to use formed mesh bags. U.S. Pat. No. 4,428,375 to Ellman, is an example of a tubular mesh bag used for supporting a spleen. U.S. Pat. No. 6,951,534, which issued to Michael J. Girard et al., discloses an example of a cardiac wrap. Bags that are created from fabric sheets, like Ellman's, have conventionally been formed using additional materials (e.g. an additional stitch to maintain the configuration of the bag). Existing mesh bags that have been knitted into complex shapes directly, like Girard's, are created by a knitting process. These bags are knitted into the desired configuration, a task accomplished only with very complicated and expensive equipment or by hand.